Simultaneous solvent extraction of a light and heavy fraction



Heavy Raff/note Sept. 23, 1969 K. o.u|'r1'| 3,468,793

SIMULTANEOUS SOLVENT EXTRACTION OF A LIGHT AND HEAVY FRACTION Filed Aug.17. 1967 'o N .2 E 9 9 8 1 E rq q Q: m

QB N) 0 N N N N Stripper Extractor Extractor t //v VEN r019 Kennefh D.U/ff/ Heavy Feed Light Raff/'nafe Lighf Fee A TTORNEYS United StatesPatent Office 3,468,793 Patented Sept. 23, 1969 US. Cl. 208-312 7 ClaimsABSTRACT OF THE DISCLOSURE Process for separating and recoveringaromatic hydrocarbons, such as benzene, from two different feedstockmixtures via a dual zone solvent extraction technique. The preferredsolvent comprises sulfolane and the extraction zones are refluxedindividually with specific nonaromatic hydrocarbon streams.

Background of the invention This invention relates to a separationprocess. It also relates to a solvent extraction process for therecovery of aromatic hydrocarbons from hydrocarbon mixtures utilizing aselective solvent. It particularly relates to a solvent extractionprocess whereby aromatic hydrocarbons are simultaneously recovered fromtwo different feedstocks utilizing a dual extraction system.

The technique of aromatic hydrocarbon separation by solvent extractionis well known in the prior art. Generally, according to a well knownprocedure, a mixture of hydrocarbons is introduced into an extractionzone at an intermediate point thereof and contacted therein with asolvent which is selective for aromatic hydrocarbons. The conditions inthe extraction zone are sufficient to produce a raflinate phasecomprising substantially all of the nonaromatic hydrocarbons in thefeedstock and an extract phase comprising the aromatic components of thefeedstock dissolved in the selective solvent. The nonaromatic raffinatephase is generally recovered and utilized in gasoline blending. Theextract phase is subse quently passed through various separation meansfor the recovery therefrom of aromatic hydrocarbons in relatively highconcentration and high purity with a residue fraction comprising leansolvent which is generally suitable for reuse in the extraction zone.One feature in the prior are process is the substantial freeing of theextract phase of substantially all of the non-aromatic componentsdissolved by the solvent. This is generally accomplished by introducinga non-aromatic hydrocarbon reflux stream, typically, comprisingnaphthenes and parafiins into the extraction zone at a pointintermediate between the feed introduction point and the extract phasewithdrawal point. This reflux phase is more volatile in the presence ofthe solvent than either of the aromatic or raffinate components of thefeedstock and in effect acts as a displacing agent for the non-aromatichydrocarbons into the raffinate stream.

Normally, in a solvent extraction process of the type describedhereinabove, the raflinate stream is recovered as a separate product andaromatic hydrocarbons are recovered as a second product stream. Both ofthese product streams have well known end uses. Accordingly, petroleumrefiners have various hydrocarbon feedstocks possessing differentcharacteristics. It is common practice to pass these feedstocks throughthe solvent extraction system in blocked-out operation so as to avoidcontamination of the various product streams with undesirablecomponents. If the volume of different feedstocks is sufficient, it isalso common practice for the prior art to build two separate anddistinct solvent extraction systems again in order to avoid crosscontamination between the various products. It would be desirable,therefore, to provide a process whereby different hydrocarbon feedstockscould be processed through the solvent extraction system with a minimumof excess equipment and with a technique which would avoid crosscontamination of the products.

Summary of the invention Therefore, it is an object of this invention toprovide a Separation process.

It is another object of this invention to provide a solvent extractionprocess for the recovery of aromatic hydrocarbons from hydrocarbonmixtures.

It is still another object of this invention to provide a process forthe recovery of aromatic hydrocarbons from two difierent feedstocks viaa dual solvent extraction technique in a facile and economic manner.

According to the practice of the present invention there is provided aprocess for separating aromatic hydrocarbons from a relatively heavyhydrocarbon mixture and from a relatively light hydrocarbon mixturewhich comprises the steps of: (a) introducing said light mixture into afirst solvent extraction zone in contact with a hereinafter specifiedlean solvent stream and a hereinafter specified light reflux streamunder conditions suflicient to produce a light rafiinate stream and anextract stream comprising solvent having aromatic hydrocarbons dissolvedtherein; (b) removing from said first zone said light rafiinate as afirst product stream; (0) introducing said heavy mixture into a secondsolvent extraction zone in contact with hereinafter specified leansolvent stream and hereinafter specified heavy reflux stream underconditions sufficient to produce a heavy raffinate stream and an extractstream comprising solvent having aromatic hydrocarbons dissolvedtherein; (d) removing from said second zone said heavy raflinate as asecond product stream; (e) passing the extract stream from said firstzone and from said second zone into a first distillation zone maintainedunder distillation conditions; (f) withdrawing from said firstdistillation zone an overhead fraction comprising relatively lightnon-aromatic hydrocarbons, a side-cut fraction comprising relativelyheavy non-aromatic hydrocarbons and a first bottoms fraction comprisingsolvent having aromatic hydrocarbons dissolved therein; (g) passing atleast a portion of said overhead fraction into said first extractionzone of step (a) as the specified reflux stream therein; (h) passing atleast a portion of said side-cut fraction into said second extractionzone of step (c) as the specified reflux stream therein; (i) introducingsaid first bottoms fraction into a second distillation zone maintainedunder conditions sufficient to produce an overhead fraction comprisingaromatic hydrocarbons and a second bottoms fraction comprising leansolvent; and, (j) returning at least a portion of the lean solvent ofstep (i) to the first and second extraction zones as specified.

Another embodiment of this invention includes the process hereinabovewherein said lean solvent comprises sulfolane.

A specific embodiment of this invention includes the process hereinabovewherein said overhead fraction of step (i) comprises a combined mixtureof aromatic hydrocarbons which were originally present in said' lightmixture and originally present in said heavy mixture.

As a broad general class, suitable feedstocks of the satisfactorypractice of this invention include fluid hydrocarbon mixtures having asufiiciently high concentration of aromatic hydrocarbons to economicallyjustify recovery of the aromatics. The present invention is particularlyapplicable to hydrocarbon feed mixtures which are different in somecharacteristic. The most applicable characteristic for the practice ofthis invention include hydrocarbon mixtures which are different in termsof boiling point. Therefore, feedstocks applicable for use in thepresent invention include a relatively heavy hydrocarbon mixture and arelatively light hydrocarbon mixture. In other words, these differentfeedstocks include a relatively low boiling aromatic hydrocarbon-comtaining feedstock and a relatively high boiling aromatichydrocarbon-containing feedstock. These difierent feedstocks preferablyshould contain at least 25% by Weight aromatic hydrocarbons and shouldhave at least one aromatic hydrocarbon type which is common between thetwo different feedstocks; although, this common expedient is notnecessarily a requirement thereof, only a preferred embodiment thereof.The suitable carbon number range of the feedstocks is from about 6carbon atoms per molecule to about 20 carbon atoms per molecule and,preferably, from about 6 to carbon atoms per molecule. One source offeedstock is debutanized reactor effluent from a catalytic reformingprocessing unit. Another source is a liquid by-product from a pyrolysisprocessing unit which has been hydrotreated to saturate diolefins andolefins and to remove other contaminants thereby producing an aromatichydrocarbon concentrate suitable for solvent extraction techniques. Anexample of a relatively light hydrocarbon feedstock include a mixture ofhexane, cyclohexane, and benzene. An example of a relatively heavyhydrocarbon feedstock include a wide boiling benzene, toluene, xylenestream mixed with the corresponding paraflins and naphthenes which hasbeen obtained from a conventional catalytic reforming unit.

The preferred solvent which may be utilized in the aromatics extractionprocess of the present invention is a solvent of a sulfolane type. Thesolvent is Well known and typically possesses a five membered ringcontaining 1 atom of sulfur and 4 atoms of carbon with 2 oxygen atomsbonded to the sulfur atom of the ring. Those skilled in the aromaticsextraction art are Well versed in in the characteristics of this type ofsolvent and more detail thereof need not be presented at this time.

Other solvents which may be included and may be satisfactorily used inthe practice of this invention are the sulfolenes, such as 2-sulfoleneand 3-sulfolene. Still other typical solvents which have a highselectivity for separating aromatic hydrocarbons from non-aromatichydrocarbons and which may be processed within the scope of the presentinvention are 2-methyl-sulfolane, 2,4-dimethyl-sulfolane,methyl-2-sulfonylether, n-aryl-3-sulfonylamine, 2-sulfonylacetate,diethyleneglycol, various polyethyleneglycols, dipropyleneglycol,various polypropyleneglycols, dimethylsulfoxide, n-methylpyrrolidone,and the like. The specifically preferred solvent for use in the'practice of the invention is sulfolane.

The aromatic selectivity of the solvent can usually be further enhancedby the addition of Water to the solvent. Preferably, the solventsutilized in the practice of this invention contain small quantities ofwater in order to increase the selectivity of the overall solvent phasefor aromatic hydrocarbon over non-aromatic hydrocarbons without reducingsubstantially the solubility of the solvent phase for aromatichydrocarbon. The presence of water in the solvent composition furtherprovides a relatively volatile material therein which is distilled fromthe solvent in the extractor stripper, more fully discussed hereinafterto vaporize the last traces of non-aromatic hydrocarbons from thesolvent stream by steam distillation. The composition of the presentinvention preferably contains from about 0.5% to about by weight waterand preferably from about 5% to about 15% by weight depending upon theparticular solvent utilized and the process conditions at which theextraction zones and extractive stripper are operated.

The dual extraction zones of the present invention are operated atelevated temperature and at sufiiciently elevated pressure to maintainthe feedstock solvent and reflux streams in liquid phase. The operatingconditions in each extraction zone may be the same or may be differentdepending upon the characteristics of the particular feedstock chargedto the particular extraction zone. Typically, suitable temperatures whenusing sulfolane as the solvent are within a range of from about 80 F. toabout 400 F., and preferably from about 175 F. to about 300 F. Suitablepressures are generally within the range I from about atmosphericpressure up to about 400 p.s.i.g.

and, preferably, from 50 to 150 p.s.i.g.

It is noted from the description of the present invention thus far thatone of the critical problems to which this invention is directed is thedisplacement of non-aromatic hydrocarbons from the extract phase of thelower end of the extraction by utilizing the technique of a nonaromaticreflux at that point. Therefore, it is a feature of the presentinvention to use a relatively light reflux material in the extractionzone which is charging the relatively light or low boiling hydrocarbonfeedstock. Conversely, it is a feature of this invention to utilize arelatively heavy reflux on the lower end of the extraction zone whichcharges these relatively heavy or high boiling hydrocarbon feedstocks tothe extraction zone. The source of the specific reflux streams utilizedherein will be more fully developed hereinbelow. In any event, thevolume of reflux material introduced into the lower end of theextraction zone should be at least 10% by volume of the extract phaseleaving the extraction zone in question in order toeifectively displacethe non-aromatic hydrocarbons from the extract. By operating in thismanner, cross-contamination of the respective raffinate stream productsis avoided.

The extract stripper is operated at moderate pressures and sufiicientlyhigh reboiler temperatures to drive all of the non-aromatic material andsome of the aromatics, water, and solvent out of the bottom portion ofthe column. Typical stripper pressures are from atmospheric pressure toabout p.s.i.g., although, generally the top of the stripper ispreferably maintained at from about 1 p.s.i.g. to about 20 p.s.i.g. Thereboiler temperature, of course, is dependent upon the composition ofthe feedstock and the solvent. The column is arranged to take anoverhead fraction, at least one side-cut fraction, and a bottomsfraction as separate product streams. Those skilled in the art from aknowledge of the prior art are well versed in the operation of astripper column and additional details thereof need not be presentedhere.

The solvent recovery column is operated at low pressures andsufiicien-tly high temperatures to distill the aro matic hydrocarbonsoverhead as a distillate fraction thereby producing a solvent. bottomsfraction which is generally suitable for reuse in both the solventextraction zones previously mentioned. Again, the choice of operatingconditions depend upon the feedstock characteristics and the compositionof the solvent. Preferably, the top of the solvent recovery column isoperated at about 100 to 400 mm. Hg absolute. These subatmosphericpressures must be employed in order to maintain a sufiiciently lowreboiler temperature to avoid thermal decomposition of the solvent;particularly When the solvent is of the sulfolane type. Preferably, thereboiler temperature should be maintained below about 360 F. when usingsaturated sulfolane as the solvent.

Thus, from the description of the present invention thus far, thepresent invention involves a solvent extraction process utilizing a dualextraction zone in a combined stripper-aromatic recovery system wherebysolvent is recovered for reuse within the process in both extractionzones and an aromatic hydrocarbon product stream is obtained whichcontains aromatic hydrocarbons which were originally present in both ofthe feedstocks.

It is another feature of this invention that the extract streams fromthe dual extraction zones are passed into a first distillation columnwhich is maintained under conditions sufficient to produce overhead adistillate fraction comprising relatively light non-aromatichydrocarbons. These conditions are also suflicient to produce as asidecut fraction a stream comprising relatively heavy nonaromatichydrocarbons. The residue or bottoms fraction from this distillationzone contains the rich solvent having dissolved therein the desiredaromatic hydrocarbons which were originally present in both of thesefeedstocks.

The overhead distillate fraction from the extractive stripper isreturned at least in part to the extIaction zone as reflux therein whichoriginally had charged to it the relatively light feed mixture.Similarly the side-cut fraction is utilized at least in part as refluxon the extraction zone which charged the relatively heavy feed mixture.

The bottoms fraction or residue from the extractive distillation zone ispassed in a solvent recovery column which is operated at low pressures,as previously men tioned, in order to separate and recover the aromatichydrocarbons from the solvent phase and to recover a lean solvent streamsuitable for reuse in both of the extraction zones.

Thus, it is seen that the present invention utilizes a dual extractionzone, a common extractive stripper column, a common solvent recoverycolumn which is related to the dual extraction zone in an interdependentmanner which effects considerable economies of operation and in capitalexpense.

The invention may be further understood with reference to the appendeddrawing which a schematic repre sentation of apparatus for practicingone embodiment of the invention.

Description of the drawing Referring now to the drawing, a relativelyheavy hydrocarbon feedstock containing aromatic hydrocarbons, such as aconventional mixed product from a conventional catalytic reforming unitcomprising benzene, toluene, and xylene mixed with correspondingnaphthenes and paraifins enters the system via line 10. Simultaneouslytherewith, a relatively light hydrocarbon feedstock, such as onecomprising hexane, cyclohexane, and benzene, enters the system via line11.

Referring now to the relatively heavy feedstock operation: the feedenters extractor column 12 via line at an intermediate point. Aqueoussulfolane as the lean solvent enters the upper portion of extractor 12via line 17 and a relatively heavy reflux stream, more fully discussedhereinafter, enters extractor 12 at a lower end thereof via line 22. Arelatively heavy rafiinate stream is withdrawn from extractor 12 vialine 19 and recovered as a separate product. An extract phase comprisingsolvent having dissolved therein aromatic hydrocarbon and also which iscontaminated with small amounts of relatively heavy non-aromatichydrocarbons, such as naphthenes and paraflins, is withdrawn fromextractor 12 via line 18.

Referring now to the extraction step of the relatively light feed: therelatively light hydrocarbon feed enters extractor 13 via line 11.Aqueous sulfolane as the lean solvent enters the extractor at an upperportion thereof via line 16 and a relatively light non-aromatic refluxstream enters extractor 13 at the lower end thereof via line 21, thesource of which is more fully developed hereinbelow. A relatively lightraffinate stream is withdrawn from extractor 13 via line 14 andrecovered as a separate product stream. An extract phase comprisingsolvent having aromatic hydrocarbons dissolved therein and which iscontaminated with minor amounts of relatively light non-aromatichydrocarbons is withdrawn from extractor 13 via line 15.

As a preferred embodiment of this invention, the relatively heavyextract phase in line 18 is passed into extractive stripper column 20 atan intermediate location therein. Similarly, the relatively lightextract phase in line 15 is introduced into extract stripper column 20at an upper point thereof. Additional solvent may be added to extractorstripper column 20 as needed, from a source not shown, in order toenhance the separation of the nonaromatic hydrocarbons from the solventcontaining the aromatic hydrocarbons. Sufficient separation conditionsare maintained in extractive stripper 20' to produce a bottoms fractioncomprising solvent having dissolved therein the desired aromatichydrocarbons which are removed from stripper 20 via line 23.

A distillate fraction comprising relatively light nonaromatichydrocarbons and minor amounts of solvent is removed via line 21 andpassed into extractor 13 at the lower end thereof as the relativelylight reflux stream, previously mentioned. A side-cut fractioncomprising relatively heavy non-aromatic hydrocarbons and minor amountsof solvent is removed via line 22 and passed into the lower portion ofextractor 12 as the relatively heavy refiux stream, previouslymentioned.

Referring now to the solvent and aromatic hydrocarbon stream in line 23;this material is passed into recovery column 24 which is maintainedunder conditions sufiicient to separate the aromatic hydrocarbons fromthe solvent phase. The aromatic hydrocarbons are concentrated as adistillate fraction and removed for recovery via line 25. It is to benoted that the material in line 25 contains, for example, benzene whichwas originally present in the heavy feed in line 10 and the light feedin line 11 and is removed from the system as a combined product stream.The operation of recovery column 24 includes the use of steam strippingin the column in order to remove the final traces of aromatichydrocarbons from the solvent. Therefore, the lower end of column 24contains the desired solvent plus water generally in sufficient amountssuch that the material withdrawn from column 24 via line 26 compriseslean solvent generally suitable for reuse in both extraction zones. Itis noted that this lean solvent stream in line 26 is split and a portionthereof is passed via line 16 into extractor 13 and another portionpassed via line 17 into extractor 12 as previously described.

Thus, it is seen that the practice of the present invention enables thesimultaneous handling of two different feedstocks which avoids thecontamination of the light raffinate phase with non-aromatichydrocarbons from the heavy feed system and enables the production of acombined aromatics stream in high concentration and high purity withoutthe necessity of either blocked-out operation or absolute duplicity ofequipment.

Preferred embodiment Therefore, from the presentation presentedhereinabove, the preferred embodiment of the invention provides aprocess for separating and recovering a combined aromatic hydrocarbonstream from two different feedstocks which comprises the steps of: (a)introducing a relatively low boiling aromatic hydrocarbon-containingfeedstock into a first solvent extraction zone and introducing ahereinafter specified low boiling reflux stream into said first zone,said first solvent extraction zone being maintained under extractionconditions, including the presence of lean solvent, sufiicient toseparate said low boiling feedstock into a slight rafiinate stream andan extract stream comprising solvent having aromatic hydrocarbonsdissolved therein and containing light non-aromatic hydrocarbons ascontaminants therein; (b) removing from said first zone said lightraflinate as a first product stream; (c) introducing a relatively highboiling aromatic hydro- 7 carbon-containing feedstock into a secondsolvent extraction zone and introducing a hereinafter specified highboiling reflux stream into said second zone, said second solventextraction zone being maintained under extraction conditions, includingthe presence of lean solvent, sufiicient to separate said high boilingfeedstock into a heavy rafiinate stream and an extract stream comprisingsolvent having aromatic hydrocarbons dissolved therein and containingheavy non-aromatic hydrocarbons as contaminants therein; (d) removingfrom said second zone said heavy rafiinate as a second product stream;(e) passing the extract stream from the first extraction zone into afirst distillation zone at the upper portion thereof and passing theextract stream from the second extraction zone into said first column atan intermediate portion thereof, said first column being maintainedunder conditions suflicient to produce an overhead fraction comprisingrelatively light non-aromatic hydrocarbons, a sidecut fractioncomprising relatively heavy non-aromatic hydrocarbons, and a firstbottoms fraction comprising solvent having aromatic hydrocarbonsdissolved therein; (f) passing at least a portion of said overheadfraction into said first extraction zone of step (a) as the specifiedreflux stream; (g) passing at least a portion of said sidecut fractioninto said second extraction zone of step (c) as the specified refluxstream therein; (h) introducing said first bottoms fraction from step(e) into a second distillation zone maintained under distillationconditions sufiicient to produce a second distillate fraction comprisingaromatic hydrocarbons and a second bottoms fraction comprising leansolvent suitable for reuse in said extraction zone; and, (i) recoveringsaid second distillate fraction.

Another preferred embodiment of this invention includes the processhereinabove wherein said solvent comprises sulfolane.

A particularly preferred embodiment of this invention is the processhereinabove wherein said aromatic hydrocarbons in said distillatefraction from the second distillation zone contains benzene.

The invention claimed:

1. Process for separating aromatic hydrocarbons from a relatively heavyhydrocarbon mixture and from a relatively light hydrocarbon mixturewhich comprises the steps of:

(a) introducing said light mixture into a first solvent extraction zonein contact with a hereinafter specified lean solvent stream and ahereinafter specified light reflux stream under conditions suflicient toproduce a light raflinate stream and an extract stream comprisingsolvent having aromatic hydrocarbons dissolved therein;

(b) removing from said first zone said light raflinate as a firstproduct stream;

(c) introducing said heavy mixture into a second solvent extraction zonein contact with hereinafter specified lean solvent stream andhereinafter specified heavy reflux stream under conditions suflicient toproduce a heavy raflinate stream and an extract stream comprisingsolvent having aromatic hydrocarbons dissolved therein;

(d) removing from said second zone said heavy raflinate as a secondproduct stream;

(e) passing the extract stream from said first zone and from said secondzone into a first distillation zone maintained under distillationconditions;

(f) Withdrawing from said first distillation zone an overhead fractioncomprising relatively light nonaromatic hydrocarbons, a side-cutfraction comprising relatively heavy non-aromatic hydrocarbons, and afirst bottoms fraction comprising solvent having aromatic hydrocarbonsdissolved therein;

(g) passing at least a portion of said overhead fraction into said firstextraction zone of step (a) as the specified reflux stream therein;

(h) passing .at least a portion of said side-cut fraction into saidsecond extraction zone of step (c) as the specified reflux streamtherein;

(i) introducing said first bottoms fraction into a second distillationzone maintained under conditions suflicient to produce an overheadfraction comprising aromatic hydrocarbons and a second bottoms fractioncomprising lean solvent; and,

(j) returning at least a portion of the lean solvent of step (i) to thefirst and second extraction zones as specified.

2. Process according to claim 1 wherein said lean solvent comprisessulfolane.

3. Process according to claim 1 wherein said overhead fraction of step(i) comprises a combined mixture of aromatic hydrocarbons which wereoriginally present in said light mixture and originally present in saidheavy mixture. I

4. Process for separating and recovering'a combined aromatic hydrocarbonstream from two different feedstocks which comprises the steps of:

(a) introducing a relatively low boiling aromatic hydrocarbon containingfeedstock into a first solvent extraction zone and introducing ahereinafter specified low boiling reflux stream into said first zone,said first solvent extraction zone being maintained under extractionconditions, including the presence of lean solvent, suflicient toseparate said low boiling feedstock into a light raffinate stream and anextract stream comprising solvent having aromatic hydrocarbons dissolvedtherein and containing light nonaromatic hydrocarbons as contaminantstherein;

(b) removing from said first zone said light raflinate as a firstproduct stream;

(0) introducing a relatively high boiling, aromatic hydrocarboncontaining feedstock into a second solvent extraction zone andintroducing a hereinafter specified high boiling reflux stream into saidsecond zone, said second solvent extraction zone being maintained underextraction conditions, including the presence of lean solvent,suflicient to separate said high boiling feedstock into a heavyraffinate streamand an extract stream comprising solvent having aromatichydrocarbons dissolved therein and containing heavy non-aromatichydrocarbons as contaminants therein;

(d) removing from said second zone said heavy raftinate as a secondproduct stream;

(e) passing the extract stream from the first extraction zone into afirst distillation zone at the upper portion thereof and passing theextract stream from the second extraction zone into said first column atan intermediate portion thereof, said first column being maintainedunder conditions suflicient to produce an overhead fraction comprisingrelatively light nonaromatic hydrocarbons, a side-cut fractioncomprising relatively heavy non-aromatic hydrocarbons, and a firstbottoms fraction comprising solvent having aromatic hydrocarbonsdissolved therein;

(f) passing at least a portion of said overhead fraction into said firstextraction zone of step (a) as the specified reflux stream;

(g) passing at least a portion of said side-cut fraction into saidsecond extraction zone of step (c) as the specified reflux streamtherein;

(h) introducing said first bottoms fraction from step (e) into a seconddistillation zone maintained under distillation conditions suflicient toproduce a second distillate fraction comprising aromatic'hydrocarbonsand a second bottoms fraction comprising lean solvent suitable for reusein said extraction zones; and,

(i) recovering said second distillate fraction.

5. Process according to claim 4 wherein said solvent comprisessulfolane.

6. Process according to claim 5 wherein said aromatic hydrocarbonscomprise single ring type aromatic hydrocarbons.

9 10 7. Process according to claim '6 wherein said single 3,262,8757/1966 (31 m :1 208-321 r g hydrocarbons comprisc bmzcne- 3,361,6641/1968 Broughton 61 a1. 208-321 References (3M HERBERT LEVINE, PrimaryExaminer v UNITED STATES PATENTS 5 2,492,787 12/1949 Davis 208-3212,921,015 1/1960 Shiras 208-412 208-318, 321, 32$;260-674

